The present invention relates generally to GPS-based vehicle guidance systems used in agricultural applications and more particularly to a method for using a single steering wheel motion input sensor to initiate multiple actions on the vehicle.
Tractors and other off-road work vehicles in the agricultural, mining and construction industries are increasingly equipped with satellite-based guidance (GPS) systems to efficiently control movement over an area. For safety purposes these systems must have an easily-operated manual override capability. The most common is to disengage the GPS whenever the operator takes control of the steering wheel, such as needed to avoid an obstacle in the vehicle path or to turn the vehicle around at the end of a row. The conventional method for detecting steering wheel movement for GPS manual override is through hydraulic sensing of the steering circuit. These methods are costly and have limited accuracy. Activating the manual override requires greater effort when the vehicle is cold than when warm. Hydraulic seal leakage can allow slow steering wheel movement to go undetected which could leave the GPS inadvertently engaged.
Another aspect of the tractors and other off-road work vehicles which require steering wheel motion detection is the automatic cancellation of turn indication signals. An operator initiates a turn signal using an on-board turn indicator switch, causing the signal to flash during the turning sequence. A series of reed switches and a simple 3-pole magnetic ring mounted on a steering shaft are conventionally used to sense the change in steering wheel position to signal the completion of a turn. While the system is well-proven, it has limited accuracy due to the limited number of magnetic poles.
It would be a great advantage to provide a single steering wheel movement detection apparatus capable of providing steering wheel movement signals to multiple systems and apparatus on the vehicle thereby reducing the spatial requirements for a sensor on the steering column. Additional benefits would be realized by a sensing apparatus capable of detecting not only steering wheel movement, but simultaneously detecting changes in the direction of steering wheel movement would provide necessary input for a broad range of vehicle navigational and control functions. Further advantages would be realized if the apparatus could provide increased accuracy over the multiple sensors that it replaces. Still further advantages would be realized if the sensing apparatus could be economically produced at significantly lower costs that the multiple sensors it replaces. These and other advantages are provided by the method and vehicle guidance system described below.